MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
General Description
The MX7705 low-power, 2-channel, serial-output ana-
log-to-digital converter (ADC) includes a sigma-delta
modulator with a digital filter to achieve 16-bit resolution
with no missing codes. This ADC is pin compatible and
software compatible with the AD7705. The MX7705 fea-
tures an on-chip input buffer and programmable-gain
amplifier (PGA). The device offers an SPI-/QSPI™-/
MICROWIRE®-compatible serial interface.
The MX7705 operates from a single 2.7V to 5.25V supply.
The operating supply current is 320µA (typ) with a 3V
supply. Power-down mode reduces the supply current to
2µA (typ).
Self-calibration and system calibration allow the MX7705
to correct for gain and offset errors. Excellent DC perfor-
mance (±0.003% FSR INL) and low noise (650nV) make
the MX7705 ideal for measuring low-frequency signals
with a wide dynamic range. The device accepts fully dif-
ferential bipolar/unipolar inputs. An internal input buffer
allows for input signals with high source impedances. An
on-chip digital filter, with a programmable cutoff and out-
put data rate, processes the output of the sigma-delta
modulator. The first notch frequency of the digital filter is
chosen to provide 150dB rejection of common-mode
50Hz or 60Hz noise and 98dB rejection of normal-mode
50Hz or 60Hz noise. A PGA and digital filtering allow sig-
nals to be directly acquired with little or no signal-condi-
tioning requirements.
The MX7705 is available in a 16-pin TSSOP package.
Benefits and Features
•
Pin Compatible and Software Compatible with the
•
•
•
•
•
•
•
•
•
AD7705
16-Bit Sigma-Delta ADC
Two Fully Differential Input Channels
0.003% Integral Nonlinearity with No Missing Codes
Interface with Schmitt Triggers on Inputs
Internal Analog Input Buffers
PGA from 1 to 128
Single (2.7V to 3.6V) or (4.75V to 5.25V) Supply
Low Power
1mW (max), 3V Supply
2µA (typ) Power-Down Current
SPI-/QSPI-/MICROWIRE-Compatible 3-Wire Serial
Interface
Ordering Information
PART
MX7705EPE+
MX7705EUE+
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN- PACKAGE
16 PDIP
16 TSSOP
MX7705EWE+
-40°C to +85°C
16 SO
+Denotes
a lead(Pb)-free/RoHS-compliant package.
Applications
Industrial Instruments
Weigh Scales
Strain-Gauge Measurements
Loop-Powered Systems
Flow and Gas Meters
Medical Instrumentation
Pressure Transducers
Thermocouple Measurements
RTD Measurements
Pin Configuration
TOP VIEW
SCLK 1
CLKIN 2
CLKOUT 3
CS 4
RESET 5
AIN2+ 6
AIN1+ 7
AIN1- 8
16 GND
15 V
DD
14 DIN
MX7705
13 DOUT
12 DRDY
11 AIN2-
10 REF-
9
REF+
TSSOP
QSPI is a trademark of Motorola, Inc.
MICROWIRE is a registered trademark of National
Semiconductor Corp.
19-3051; Rev 5; 6/15
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
Absolute Maximum Ratings
V
DD
to GND ..............................................................-0.3V to +6V
All Other Pins to GND.................................-0.3V to (V
DD
+ 0.3V)
Maximum Current Input into Any Pin ..................................50mA
Continuous Power Dissipation (T
A
= +70°C)
TSSOP (derate 9.4mW/°C above +70°C) ...................755mW
SO (derate 9.5mW/°C above +70°C) .......................761.9mW
PDIP (derate 10.5mW/°C above +70°C) ..................842.1mW
Operating Temperature Range ..........................-40°C to +85°C
Storage Temperature Range .............................-60°C to +150°C
Junction Temperature ......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Electrical Characteristics
(V
DD
= 3V or 5V, V
GND
= 0V, V
REF+
= 1.225V for V
DD
= 3V and V
REF+
= 2.5V for V
DD
= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1µF, C
REF
- to GND = 0.1µF, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
DC ACCURACY
Resolution (No Missing Codes)
Output Noise
Integral Nonlinearity
Unipolar Offset Error
Unipolar Offset Drift
Bipolar Zero Error
Bipolar Zero Drift (Note 2)
Positive Full-Scale Error
Full-Scale Drift
Gain Error
Gain Drift
Bipolar Negative Full-Scale Error
Bipolar Negative Full-Scale Drift
(Note 2)
ANALOG INPUTS (AIN1+, AIN1-, AIN2+, AIN2-)
Unipolar input range
AIN Differential Input Voltage
Range (Note 7)
Bipolar input range
Unbuffered
AIN Absolute Input Voltage
Range (Note 8)
Buffered
AIN DC Leakage Current
Unselected input channel
0
-V
REF
/
GAIN
GND -
30mV
GND +
50mV
V
REF
/
GAIN
V
V
REF
/
GAIN
V
DD
+
30mV
V
V
DD
-
1.5V
1
nA
INL
Gain = 1, unbuffered
After calibration
(Note 2)
After calibration
Gain = 1 to 4
Gain = 8 to 128
After calibration
(Notes 2, 4)
After calibration
(Notes 2, 6)
After calibration
Gain = 1 to 4
Gain = 8 to 128
(Note 1)
0.5
(Note 1)
0.5
0.1
(Notes 1, 3)
0.5
(Notes 1, 5)
0.5
±0.003
1
0.6
16
Tables 1, 3
±0.003
Bits
µV
%FSR
µV
µV/°C
µV
µV/°C
µV
µV/°C
µV
ppm of
FSR/°C
%FSR
µV/°C
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
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Maxim Integrated | 2
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
Electrical Characteristics (continued)
(V
DD
= 3V or 5V, V
GND
= 0V, V
REF+
= 1.225V for V
DD
= 3V and V
REF+
= 2.5V for V
DD
= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1µF, C
REF
- to GND = 0.1µF, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
SYMBOL
Gain = 1
AIN Input Capacitance
Gain = 2
Gain = 4
Gain = 8 to 128
AIN Input Sampling Rate
f
s
Gain = 1 to 128
Gain = 1
V
DD
= 5V
Input Common-Mode Rejection
CMR
V
DD
= 3V
Gain = 2
Gain = 4
Gain = 8 to 128
Gain = 1
Gain = 2
Gain = 4
Gain = 8 to 128
Normal-Mode 50Hz Rejection
Normal-Mode 60Hz Rejection
Common-Mode 50Hz Rejection
Common-Mode 60Hz Rejection
EXTERNAL REFERENCE (REF+, REF-)
REF Differential Input Voltage
Range (Note 9)
REF Absolute Input Voltage Range
REF Input Capacitance
REF Input Sampling Rate
f
s
Gain = 1 to 128
V
REF
V
DD
= 4.75V to 5.25V
V
DD
= 2.7V to 3.6V
1.0
1.00
GND
10
f
CLKIN
/
64
2
V
DD
= 4.75V to 5.25V
V
DD
= 2.7V to 3.6V
DIN,
CS, RESET
SCLK
250
500
±1
5
0.8
0.4
3.5
1.75
V
DD
V
V
pF
MHz
For filter notches of 25Hz, 50Hz,
±0.02
×
f
NOTCH
For filter notches of 20Hz, 60Hz,
±0.02
×
f
NOTCH
For filter notches of 25Hz, 50Hz,
±0.02
×
f
NOTCH
For filter notches of 20Hz, 60Hz,
±0.02
×
f
NOTCH
96
105
110
130
105
110
120
130
98
98
150
150
dB
dB
dB
dB
dB
CONDITIONS
MIN
TYP
34
38
45
60
f
CLKIN
/
64
MHz
pF
MAX
UNITS
DIGITAL INPUTS (DIN, SCLK,
CS, RESET)
Input High Voltage
Input Low Voltage
Input Hysteresis
Input Current
Input Capacitance
V
IH
V
IL
V
HYST
I
IN
V
V
mV
µA
pF
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Maxim Integrated | 3
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
Electrical Characteristics (continued)
(V
DD
= 3V or 5V, V
GND
= 0V, V
REF+
= 1.225V for V
DD
= 3V and V
REF+
= 2.5V for V
DD
= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1µF, C
REF
- to GND = 0.1µF, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
CLKIN INPUT
CLKIN Input High Voltage
CLKIN Input Low Voltage
CLKIN Input Current
V
CLKINH
V
CLKINL
I
CLKIN
DOUT and
DRDY,
I
SINK
= 800µA
CLKOUT,
I
SINK
= 10µA
DOUT and
DRDY,
I
SINK
= 100µA
CLKOUT,
I
SINK
= 10µA
DOUT and
DRDY,
I
SOURCE
= 200µA
CLKOUT,
I
SOURCE
= 10µA
DOUT and
DRDY,
I
SOURCE
= 100µA
CLKOUT,
I
SOURCE
= 10µA
4.0
4.0
V
V
DD
-
0.6V
V
DD
-
0.6V
±10
9
-1.05
×
V
REF
/
GAIN
-1.05
×
V
REF
/
GAIN
0.8
×
V
REF
/
GAIN
1.05
×
V
REF
/
GAIN
1.05
×
V
REF
/
GAIN
2.1
×
V
REF
/
GAIN
µA
pF
V
DD
= 4.75V to 5.25V
V
DD
= 2.7V to 3.6V
V
DD
= 4.75V to 5.25V
V
DD
= 2.7V to 3.6V
3.5
2.5
0.8
0.4
±10
V
V
µA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DIGITAL OUTPUTS (DOUT,
DRDY,
CLKOUT)
0.4
0.4
V
0.4
0.4
V
DD
= 5V
Output Voltage Low
V
OL
V
DD
= 3V
V
DD
= 5V
Output Voltage High
V
OH
V
DD
= 3V
Tri-State Leakage Current
Tri-State Output Capacitance
SYSTEM CALIBRATION
Full-Scale Calibration Range
I
L
C
OUT
DOUT only
DOUT only
GAIN = selected PGA gain (1 to 128)
(Note 10)
V
Offset Calibration Range
GAIN = selected PGA gain (1 to 128)
(Note 10)
V
Input Span
GAIN = selected PGA gain (1 to 128)
(Notes 10, 11)
V
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Maxim Integrated | 4
MX7705
16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADC
Electrical Characteristics (continued)
(V
DD
= 3V or 5V, V
GND
= 0V, V
REF+
= 1.225V for V
DD
= 3V and V
REF+
= 2.5V for V
DD
= 5V, V
REF-
= GND, external f
CLKIN
=
2.4576MHz, CLKDIV bit = 0, C
REF+
to GND = 0.1µF, C
REF
- to GND = 0.1µF, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
POWER REQUIREMENTS
Power-Supply Voltage
V
DD
Unbuffered
f
CLKIN
=1MHz,
gain =1 to 128
Buffered,
f
CLKIN
=1MHz,
gain =1 to 128
V
DD
= 5V
V
DD
= 3V
V
DD
= 5V
V
DD
= 3V
V
DD
= 5V,
gain = 1 to 4
V
DD
= 5V,
gain = 8 to 128
V
DD
= 3V,
gain = 1 to 4
V
DD
= 3V,
gain = 8 to 128
V
DD
= 5V,
gain = 1 to 4
V
DD
= 5V,
gain = 8 to 128
Buffered,
f
CLKIN
= 2.4576MHz
V
DD
= 3V,
gain = 1 to 4
V
DD
= 3V,
gain = 8 to 128
Power-down mode
(Note 13)
Power-Supply Rejection Ratio
PSRR
V
DD
= 4.75V to 5.25V
V
DD
= 2.7V to 3.6V
(Note 15)
400
40
V
DD
= 5V
V
DD
= 3V
(Note 14)
(Note 14)
2500
60
2.70
5.25
0.45
0.32
0.7
0.6
0.6
0.85
0.4
0.6
0.9
1.3
0.7
1.1
16
8
µA
dB
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Unbuffered,
f
CLKIN
= 2.4576MHz
Power-Supply Current (Note 12)
I
DD
mA
EXTERNAL CLOCK TIMING SPECIFICATIONS
CLKIN Frequency
Duty Cycle
f
CLKIN
kHz
%
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